Subject: Laser Circuit
From: Christopher Ellenor <[email-masked]>
To: Alan Stummer <[email-masked]>, Rockson Chang <[email-masked]>
Cc: Adam Weir <[email-masked]>
Date: Tue, 20 Jan 2009 15:21:36 -0500 (EST)

Hi Alan -

I hope I've got everything you wanted here.  Thanks again for taking this 
on.

Find attached the diagram for our old locking circuit.  As I said, we 
trust you with any modifications.

Here is a copy of the manual for the laser controller:

http://www.laser2000.de/fileadmin/Produktdaten/NFL/Datenbl%E4tter/6000_Manual_RevH.pdf

Currently, the output of the circuit I sent is T'd between the Vortex 
current modulation input and the slower integrating circuit which produces 
the input for the Vortex "frequency" input.  The diagram of that I have in 
the notebook is an op-amp with a 4.7uF cap across the top, and a switch in 
parallel (also across the top).  Into the opamp comes a 220k resistor, and 
on the output is a 10k resistor.

The frequency gain to the laser can be set to "high" or "low" by 
computer.. we usually run it on low and that works ok.

The photodiode signals range from about 40-200mV p-p, but we lock them 
close to zero anyway.

As an input to the "modulation input" we use a triangle wave at around 1 
Hz with a p-p amplitude of around 10V.  It would be handy to have this 
built into the board as you suggested.  It would be convenient to be able 
to switch the output of the circuit between the oscillator and the 
feedback output.  If this proves to be at all difficult, we currently do 
this with an external oscillator which seems to break with some 
regularity.  We should also be able to T off the oscillator output to 
create an X-Y trace on the oscilloscope.

Just to fill you in, this is the routine we're used to using:

1)  Turn current and frequency feedbacks off

2)  Turn on oscillator, adjust laser frequency on the front panel of the 
laser driver to find the transition on the screen.

3)  Turn off oscillator, turn on current feedback

4)  Adjust pot to lock to correct part of spectroscopy curve (this sets 
the comparison voltage with that +/- 6.8 V apparatus, I think)

5)  Engage slower frequency feedback circuit.

We will use two of these, and I imagine the lattice experiment could want 
two as well...  I'll ask them once we have a design.

Thanks again,

Chris

-- 
*********************************************************************
Chris Ellenor, PhD Candidate
http://www.physics.utoronto.ca/~ellenor